WHEN you are up against the tallest man ever to play professional tennis, a giant of 6ft 11 inches who has the wingspan of an albatross and the hardest serve in the game, what do you do?

Hide in the dressing-room would be the answer for most of us, although for anyone brave enough to take to the court against Ivo Karlovic, the first thought might be to try to get under his feet by playing low balls close to him. Or, bearing in mind that the Croatian is now a veteran of 36, you might contemplate trying to tire him out by playing long rallies.

Only with a serve like that, and a forehand return of almost equal ferocity, he simply does not do long rallies. And in any event, Karlovic, despite his advancing years, has looked livelier and more athletic than ever in these Championships.

So what's the answer? For Andy Murray, it was the lob. And it was a winning answer too.

Time and time again, as Karlovic used his new-found athleticism to race to the net and try to crowd Murray out, the Scot lofted the ball improbably high, sending it soaring out of the reach of his skyscraper of an opponent then back to land in the far corner of the court. It was a tactic as successful as it was implausible, and, along with Murray's peerless return of serve, the key to his four-set victory.

We used to call this sort of thing lateral thinking, but in this case it was really vertical thinking. You can't go through an obstacle like Karlovic. You can't go past him that easily or that often. The only way is over.

Once Murray pulled off the trick for the 15th or 20th time, it all seemed so obvious. Even so, to pull it off required the most exquisite execution, as the No 3 seed played his best tennis of the tournament so far.

He had to do so, too, because Karlovic was by far his most dangerous opponent to date. True, Murray also dropped a set against Andreas Seppi in Saturday's third round, but he only really had to dig himself out of a hole once before resuming command. Against Karlovic he had to dig in right to the end of the three-hour-three-minute contest.

The match had begun in an almost soporific atmosphere as the Centre Court crowd indulged in a spot of mid-afternoon relaxation after the latest chapter of Williams versus Williams. The Royal Box was almost empty as players came on to court, though it was soon back close to capacity, which meant we got a glimpse of Ilie Nastase - full name Tennis Legend Ilie Nastase - in his Latin American dictator costume.

It wasn't the navy blue one he wore last year, by the way, but the cream-with-gold-braiding affair. It is actually something to do with his status in the Romanian army, and he is entitled to wear it, but he still looks daft in it - like an ice-cream salesman with a massively inflated idea of his own importance, which is apparently how most dictators start out in life anyway.

Back on court, Murray started out in particularly fine form. He had done so in his previous three matches too, but in the first set his first serve was exceptionally good. It dipped only a little in the tiebreak, which he still managed to take thanks to one of a score or more of unforced errors committed by Karlovic over the first hour and a half of the match.

The No 23 seed recovered instantly from that setback to serve one of his many aces in the opening point of the second set. Was that normal service resumed? Or should we say abnormal service, given the peculiar angles from which Karlovic, thanks to his height, fires down balls at his opponents?

Thankfully for Murray, no it wasn't, as the Croatian then had a minor attack of nerves over the next few points to drop serve. With his nose in front, Murray stayed just ahead in the second set, and that should have been that, with a simple third set to come.

Instead, Karlovic, who had lost all five previous meetings with Murray and had only ever previously won a set against him in a tiebreak, hit back in style to take the third. After that snoozy start, Centre Court was wide awake with anxiety as the match went into a fourth set and the home favourite faced his first serious threat of the tournament. He faced it down, but for the first time in the tournament there was more than a little feeling of relief in the crowd's celebrations at the end.